What if even after a restart of excel, this does not “take”? See whether in the registry the key CURRENT_USER\Software\Microsoft\Office\14.0\Excel\Resiliency\DisabledItems contains the path to your powerpivot add-in,like here:

This 30-sec video shows how to cycle through optional meeting time slots: While keeping an eye on the (red underlined) time slot currently polled, click green checkmark or red cross, you will be moved through the messages automatically:

Takes merely a minute, a few mouse clicks, hardly any mouse moves, and will clean up your inbox and send your vote to me at the same time.